BEAM has a 'busy wait' feature. Schedulers with no jobs to do will remain active so they can respond to new jobs faster. You can turn this down so that the schedulers go to sleep quicker, reducing CPU usage.

From http://erlang.org/doc/man/erl.html:

  +sbwt none|very_short|short|medium|long|very_long

  Sets scheduler busy wait threshold. Defaults to medium. The threshold
  determines how long schedulers are to busy wait when running out of work
  before going to sleep.